Hydraulically actuated adaptive braking system using a single fluid

ABSTRACT

A hydraulic adaptive braking system is disclosed which uses a single fluid to both actuate the brakes of the vehicle and to provide a power assist to the vehicle operator when the brakes are applied. The system includes a brake booster which utilizes pressurized fluid from the vehicle&#39;&#39;s power steering pump to develop braking pressure which is communicated to the brakes of the vehicle. Adaptive braking valve means are located in both the front and the rear brake lines and include electrically operated valve means which control fluid communication between the booster, the brakes of the vehicle and a fluid reservoir. When an incipient skid condition is sensed, the electrically operated valve means terminate fluid communication between the booster and the vehicle&#39;&#39;s brakes, and then initiates communication between the vehicle&#39;&#39;s brakes and the aforementioned reservoir to permit braking pressure at the brakes of the vehicle to decay. When the incipient skid condition terminates, the electrically operated valve means again communicates braking pressure to the vehicle&#39;&#39;s brakes.

United States Patent 91 Lewis et a1.

[451 Sept. 25, 1973 1 HYDRAULICALLY ACTUATED ADAPTIVE BRAKING SYSTEM USllNG A SINGLE FLUID [75] Inventors: Richard L. Lewis; Jerome T. Ewald; Martin A. Shields, all of South Bend, Ind.

[73] Assignee: The Bendix Corporation, South Bend, Ind.

22 Filed: Sept. 13,1971

211 App]. No.: 179,919

Williams 303/21 F Pasek et a1. 303/21 F Primary Examiner-Duane A. Reger Attorney-Ken C. Decker et a1.

[ 5 7 1 ABSTRACT A hydraulic adaptive braking system is disclosed which uses a single fluid to both actuate the brakes of the vehicle and to provide a power assist to the vehicle operator when the brakes are applied. The system includes a brake booster which utilizes pressurized fluid from the vehicles power steering pump to develop braking pressure which is communicated to the brakes of the vehicle. Adaptive braking valve means are located in both the front and the rear brake lines and include electrically operated valve means which control fluid communication between the booster, the brakes of the vehicle and a fluid reservoir. When an incipient skid condition is sensed, the electrically operated valve means terminate fluid communication between the booster and the vehicle s brakes, and then initiates communication between the vehicles brakes and the aforementioned reservoir to permit braking pressure at the brakes of the vehicle to decay. When the incipient skid condition terminates, the electrically operated valve means again communicates braking pressure to the vehicles brakes.

14 Claims, 5 Drawing Figures u \Qv PATfiNlEnstrzsms 3.7s1.140

sum 1 or 4 INVEN RICHARD L. LE JEROME T. EWALD F! G. 2 BYfiMflRTIN A. SHIELDS ATTORNEY PATENIEI] SEP2 5 I873 SHEET 3 BF 4 INVENTOR. RICHARD 1.. LEWIS JEROME T. EWALD BY MARTIN A. SHIELDS ATTORNEY m2 v O n ll-ion? ms mm WW in! v 1. un a i l!!! I PATENTED saw u or 4 INVENTOR.

RICHARD L. LEWIS JEROME T. EWALD BY MARTIN A.. SHIELDS ATTORNEY IIYDRAULICALLY ACTUATED ADAPTIVE BRAKING SYSTEM USING A SINGLE FLUID BACKGROUND OF THE INVENTION This invention relates to a hydraulically powered adaptive braking system for automotive vehicles.

While many automotive adaptive braking systems have been proposed before, most of these systems have not been widely used, mainly because all of the adaptive braking systems which have been proposed in the prior art have been very expensive to manufacture. One reason why prior art adaptive braking systems have been expensive is that they have required two separate fluid systems for brake actuation. For example, adaptive braking systems currently on the market have one hydraulic system requiring brake fluid to actuate the vehicles brakes, and another pneumatic system which operates the adaptive braking system and which provides a power assist to the vehicle operator. Adaptive braking systems have been proposed in which power steering fluid is used to provide a braking assist to the vehicle operator, but thesesystems still retain two separate hydraulic systems. To simplify design of an adaptive braking system, it is desirable to provide a system in which a common fluid is used to both actuate the brakes of the vehicle and also to provide a power assist to the vehicle operator. These systems have not heretofore been developed because of a number of problems. One of these problems has been the difficulty of designing a common fluid system which provides fail-safe capability at least equal to the fail-safe capability of existing braking systems.

SUMMARY OF THE INVENTION Therefore, an important object of our invention is to provide an automotive adaptive braking system which utilizes a single fluid.

Another important object of our invention is to provide a common fluid adaptive braking system which has fail-safe capability at least equal to existing two-fluid systems.

Another important object of our invention is to simplify the design of an adaptive braking system.

Another important object of our invention is to provide a hydraulic brake booster which combines the functions of existing master cylinders and brake boosters.

Still another important objectof our invention is to provide a simple adaptive braking control valve.

DESCRIPTION or THE DRAWINGS FIG. 1 is a schematic illustration of an adaptive braking system made pursuant to the teachings of our present invention;

FIG. 2 is a transverse cross-sectional view of a brake booster made pursuant to the teachings of our present DETAILED DESCRIPTION Referring now to the drawings, an adaptive braking system generally indicated by the numeral 10 includes a brake booster 12 actuated by the normal pedal 14 mounted in the operators compartment of the vehicle. An inlet port 16 of the booster 121 is communicated to the outlet or high pressure side of the vehicles power steering pump 15. The booster 12 includes an outlet port 18 communicated to the inlet of the vehicle's power steering gear 20. The outlet of the gear 20 is communicated to a reservoir (not shown) which is communicated to the inlet of the pump 15.

The booster 12 includes a housing 22 defining a first bore 24 and a second bore 26 therewithin, each of which communicate into a common pressure chamber 28. A primary piston 30 and a secondary piston 32 are slidably mounted in the bore 24 and define a primary chamber 34 between the pistons 30 and 32 and a secondary chamber 36 between the end of the piston 32 and the end of the bore 24. A caged spring assembly generally indicated by the numeral 38 is disposed between the pistons 30 and 32 and yieldably maintains the latter a predetermined distance apart. A bracket 40 is carried on the end of the piston 30 and a spring 42 yieldably urges the pistons 30 and 32 as a unit to the right viewing FIG. 3, maintaining the bracket 40 in engagement with the end wall of the housing 22, thereby establishing the brake released position of the booster 12. Of course, the force exerted by the caged spring assembly 38 maintaining the piston 30 and 32 apart is greater than the force exerted by the spring 42; however, a piston stop 44 is also provided to prevent the piston 32 from moving too great a distance when the booster is released.

First and second reservoirs 46 and 48 are carried by the housing 22 and each is provided with a removable closure member 50, 52, so that the fluid pressure level in the reservoir 46 or 48 may be inspected and replenished if necessary. A passage 54 communicates the reservoirs 46 and 48 with one another, and an outlet port 56 communicates the reservoirs 46 and 48 with the aforementioned reservoir (not shown) at the inlet or low pressure side of the power steering pump 15. Compensating ports 58, 60, are provided which communicate the reservoir 46, 48 with corresponding chambers 36, 24, respectively..As is well known to those skilled in the design of master cylinders, fill ports 62, 64 communicate the reservoirs 46, 48 with annular chambers 66, 68 defined between the outer circumferential surface of thepiston 32, 30 and the wall of the bore 24.

A spool valve 70 is slidably mounted in the bore 26 and is provided with spaced lands 72, 74 and 76 which cooperate with corresponding lands 78, and 80 on the wall of the bore 26 to define grooves 80, 82, 84 and 86. The inlet port 16 communicates with the groove 82, and the outlet port 18 communicates with the groove 80. Another outlet port 88 communicates with the groove 84, as do passages 90 and 92 which communicate the pressure chamber 28 with the groove 84. Still another passage 94 communicates the groove 86 with the reservoir 48. As is well known to those skilled in the art, movement of the spool valve 70 controls communication between the grooves 80, 82, 84 and 86 in a manner which will] be described hereinafter. A return spring 96 yieldably urges the spool valve 70 to the right viewing FIG. 3, maintaining the stop ring 98 carried on the left hand end of the spool valve 70 in engagement with a shoulder provided on the wall of the bore 26.

One end of an operator-operated input rod 100 is slidably received in a blind bore 102 provided in the right hand end of the piston 30 and the other end of the input rod 100 is connected to the brake pedal 14 disposed in the operators compartment of the vehicle. A spring 104 yieldably urges a bracket 106 which is slidable on the rod 100 into engagement with a retainer 108 secured to the rod 100. A first pivot 110 connects one end of a pair of levers 1 12 to the bracket 40 carried by the piston 30 and a second pivot 114 secures the other end of the levers 112 to a cap member 116 which is slidably mounted on the end of the spool valve 70. A third pivot 115 connects levers 112 to bracket 106. Details of the construction and operation of the mechanism which includes levers 112 are more completely described in U.S. Pat. No. 3,603,209, owned by the assignee of the present invention and incorporated herein by reference. A spring 118 normally maintains the cap member 116 away from openings 120 provided in the spool valve 70 to thereby permit fluid communication between the'passage 92 and the pressure chamber 28. However, when a manual brake application is initiated, the cap member 116 moves to the left viewing FIG. 3 to close the ports 120, to prevent an abrupt communication of fluid pressure into pressure chamber 28 after initiation ofa manual brake application, as will be hereinafter described.

Conduits 124 and 122 communicate the chambers 24 and 36 to adaptive braking valve means 126 and 128, respectively. The outlet of adaptive braking valve means 126 is communicated to the front wheel disc brakes 130 of the vehicle, while the outlet of the adaptive braking valve means 128 is communicated to the rear wheel drum brakes 132. Since the internal components of both the adaptive braking valve means 126 and 128 are identical, only the valve means 126 will be described in detail. The adaptive braking valve means 126 includes a housing 134 having an inlet port 136 communicated with the conduit 124 and an outlet-port 138 communicated to the front wheel brakes 130. Passage means generally indicated by the numeral 140 normally communicates the inlet port 136 with the outlet port 138. A solenoid valve generally indicated by the numeral 142 includes an armature 144 and an actuating coil 146. The armature 144 carries a sphere 147 which is adapted to sealingly engage a valve seat 148 which forms a part of the passage means 140. A spring 150 normally urges the armature 144, and therefore the sphere 147, away from the valve seat 148, to thereby maintainthe solenoid valve 142 in a normally open condition to permit substantially uninhibited fluid communication between the inlet port 136 and the outlet port 138. Valve housing 134 further includes another outlet port 152 which is communicated with the outlet port 56 of the reservoir 46 and with the reservoir (not shown) at the low pressure side of the pump by conduit 154. Passage means generally indicated by the numeral 156 within the valve means 134 communicates the outlet port 152 with the outlet port 138. A solenoid valve generally indicated by the numeral 158 includes an armature 160 and a coil 162. A sphere 164 is carried by the armature 160 and is normally urged into sealing engagement with a valve seat 166 forming a pan of the passage means 156 by a spring 168, to thereby maintain the solenoid valve 158 in a normally closed condition.

Each of the solenoid valves I42 and I58 is provided with leads I68. 170, respectively. for connecting their corresponding coils I46, 162 with an electronic control unit (not shown). The electronic control unit is constructed to sense an incipient skid of one or more of the vehicles wheels in accordance with the teaching of US. Pat. No. 3,494,671, owned by the assignee of the present invention and incorporated herein by reference. Of course, those skilled in the art will readily appreciate that any appropriate logic may be incorporated into the control unit which actuates the solenoid valves 142, 158.

Housing 134 further includes another inlet port 172 which is communicated to the outlet port 88 on the booster 12 by another conduit 174. A check valve 176 prevents communication between the port 172 and the passage means 140 unless the fluid pressure level at the inlet port 172 is higher than the fluid pressure level in the passage means 140. Of course, those skilled in the art will also recognize that the conduit 174 also communicates a corresponding port on the adaptive braking control valve means 128 with the port 88 on the booster 12. Similarly, another conduit 178 communicates a port on the valve means 128 corresponding with the port 152 on the valve means 126 with the reservoir at the low pressure side of the pump 15. It will also be noted that the reservoirs 46, 48 and the reservoir (not shown) at the inlet of the pump 15 are interconnected in such a way that a common reservoir at substantially the same fluid pressure level is provided. However, the reservoir 46 is segregated from the reservoir 48 so that in the case of loss of fluid from one of the reservoirs 46, 48 the other reservoir will be unaffected.

MODE OF OPERATION The various complements of the brake booster 12 are illustrated in FIGS. 3 and 4 in the positions which they assume when the brakes of the vehicle are released. In this position, the spool valve is so disposed that substantially uninhibited fluid communication is permitted between the grooves 82 and 80, to permit free flow of fluid throughthe booster between the pump 15 and the vehicles power steering gear 20. Similarly, it will be noted that fluid communication between the grooves 82 and 84 is prevented, and fluid communication between the grooves 84 and 86 is permitted, thereby communicating the pressure chamber 28 and the conduit 174 to the reservoir 48 through the grooves 84 and 86 and the passage 94. When a brake application is effected, the operator-operated input rod is moved to the left, thereby pivoting the levers 112 about the first pivot 110. Movement of the levers 112 shifts the spool valve 70 to the left, viewing FIG. 3, thereby closing the gap between the lands 72 and 78 to restrict flow of fluid between the grooves 82 and 80, to permit the pressure level in the groove 82 to increase. Simultaneously, the land 74 is lapped with the land 76 to terminate fluid communication between the grooves 84 and 86 to thereby terminate fluid communication between the pressure chamber 28 and the reservoir 48. As the valve shifts, the lands 74 and 78 are opened to permit the high pressure fluid being developed in the groove 82 to be communicated into the groove 84. High presssure fluid in the groove 84 is communicated into the pressure chamber 28 through the passages 90, 92 and 120. High pressure fluid in the pressure chamber 28 acts upon the right hand end of the piston 30 to urge the latter to the left viewing FIG. 3. Because of the construction of the caged spring 38, movement of the pis ton 30 will be transmitted to the piston 32 yieldably urging the latter to the left viewing FIG. 3. As the pistons 30, 32 shift, the annular seals 180, 182 on the forwardmost ends of the pistons close the compensating ports 60 and 58 to terminate fluid communication between the reservoir 46 and the chamber 36 and between the reservoir 48 and the chamber 46. Further movement of the piston 32 develops fluid pressure in the chamber 36, while further movement of the piston 30 partially collapses the caged spring 38 to develop fluid pressure in the chamber 24. Pressurized fluid developed in the chambers 24 and 36 are delivered to adaptive braking valve means 126 and 128, respectively, by conduits 124 and 122. Unless an adaptive braking cycle is initiated, substantially uninhibited fluid communication is permitted through the adaptive braking valve means 126, 128 to the front and rear brakes 130, 132 of the vehicle to initiate a brake application.

Referring now to FIG. 5, in a normal brake applica tion substantially uninhibited fluid communication through the valve 126 between the inlet port 136 and the outletport 138 through the passage means 140 is' permitted, while fluid communication between the outlet ports 138 and 152 through the passage means 156 is prevented. Since the groove 84 is communicated with the high pressure fluid in the groove 82, high' pressure fluid is communicated to the inlet port 172 of the valve means 126 through the outlet port 88 on the booster 12 and the conduit 174. However, the check valve 176 prevents fluid communication between the passage means 140 and the inlet port 172. When the electronic control unit senses an incipient skid condition of the brakes controlled by the adaptivebraking control valve 126, the electronic control unit actuates the solenoid valves 142 and 158 to terminate fluid communication through the passage 140 and initiate fluid communication through the passage 156. Therefore, the front wheel brakes 130 of the vehicle are isolated from the high pressure ,fluid in the chamber 24, and the braking pressure in the front wheel brakes 130 is communicated to the low pressure reservoir through conduit 154 thereby reducing the braking pressure delivered to the brakes 130 to permit the front wheels'of the vehicle to accelerate. When the front wheels of the vehicle have accelerated to a predetermined value, the electronic control unit signals the solenoid valves 158 and 142 to terminate communication through the passage means 156 and again inititate fluidcommunication through the passage means 140 to build braking pressure in the brakes 130. This action continues for an indefinite number of cycles, until the vehicle is brought to a safe stop.

It will be noted that since the chamber 24 has a finite volume, additional high pressure fluid must be provided to the adaptive braking control valve 126 as the latter cycles for more than a very few times. Since high pressure fluid is being communicated to the inlet port 172 through the conduit 174 and outlet port 88 of the 1 booster, the check valve 176 permits fluid communication between the inlet port 172 and the passage means 140 whenever the pressure delivered to the inlet port 136 is less than the pressure delivered to the inlet port 172 by more than a predetennined amount. Therefore, the adaptive braking valve means 126 may cycle for an indefinite number of cycles. High pressure fluid from the groove 84 in the brake booster 12 is thereby permitted to make up" or replenish the high pressure fluid being depleted from the chamber 24 by cycling of the adaptive braking valve means.

If the power steering pump 15 should fail, or if one of the conduits interconnecting the power steering pump 15, the gear 20, and the booster 12 should rupture, the increased actuation force required by the vehicle operator collapses the spring 104 to permit the end of the control rod to engage the end of the blind bore 102. A direct link is thereby provided between the piston 30 and the brake pedal 14, to permit the pistons 30 and 32 to actuate manually in a manner similar to that effected by a conventional split system master cylinder. As described hereinabove, when a manual brake application is initiated, the cap 116 slides relative to the spool valve 70 to close the passages 120, to thereby prevent an abrupt communication of high pressure fluid into the pressure chamber 28 in case fluid pressure should suddenly be delivered to the booster 12.

It will also be noted that if any conduit in the system ruptures, except for the conduits 122 and 124 and the conduits connecting the valves 1.26 and 128 to the brakes and 132, thereby permitting fluid to flow from the system, the fluid disposed in the reservoirs 46 and 48 will be relatively unaffected since they are isolated from the reservoir (not shown) at the inlet of the power steering pump 15. Similarly, if one of the conduits 122 or 124 should rupture, permitting the fluid content of one of the reservoirs 46 or 48 to become depleted, the fluid in the other reservoir 46 or 48 and in the reservoir (not shown) at the inlet of the power steering pump 15 will remain unaffected. Therefore, only one set of the brakes 130 or 132 will be lost, and pressurized fluid may still be delivered from the power steering pump 15 into the braking chamber 28 to effect a powered brake application of a single set of the vehicles brakes. Therefore, the braking system of our invention provides fail-safe capabilities equal to that of a conventional split system master cylinder actuated by a conventional pneumatic brake booster.

We claim: 1. In a vehicle hydraulic braking system: a pressure source and reservoir means; hydraulic boost means in fluid communication with said pressure source and with said reservoir means;

said boost means including fluid pressure responsive means definingapressure chamber and another chamber, said another chamber being communicated to said reservoir means; means communicating said another chamber to a corresponding brake of the vehicle; and

operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber;

said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through said conduit means; and

control means responsive to an incipient skidding condition of a vehicle wheel for operating said adaptive braking valve means.

2. The invention of claim 1:

said adaptive braking valve means having a first port communicated to said another chamber, a second port communicated to the brakes of the vehicle, and a third port communicating said electrically operated valve means to said pressure source upon actuation of said valve means.

3. The invention of claim 2:

said adaptive braking valve means having a fourth port communicating said adaptive braking valve means with said reservoir means.

4. The invention of claim 1:

said adaptive braking valve means having a first port communicated to said another chamber, a second port communicated to the vehicle brakes, and an other port communicated to said reservoir means.

5. In a vehicle hydraulic braking system:

a pressure source and reservoir means;

hydraulic boost means in fluid communication with said pressure source and with said reservoir means;

said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means;

means communicating said another chamber to a corresponding brake of the vehicle; and

operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber;

said pressure responsive means including means dividing said another chamber into first and second sections, each of said sections being communicated to said reservoir means;

said communicating means including first conduit means communicating one of said sections to at least one of the brakes of the vehicle and second conduit means communicating the other section to the remaining brakes of the vehicle;

first and second adaptive braking valve means, each of said adaptive braking valve means being communicated to a corresponding one of said conduit means for controlling fluid communication therethrough; and

control means responsive to an incipient skidding condition of a corresponding vehicle wheel for operating said adaptive braking valve means.

6. In a vehicle hydraulic braking system:

a pressure source and reservoir means;

hydraulic boost means in fluid communication with said pressure source and with said reservoir means;

said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means;

means communicating said other chamber to a corresponding brake of the vehicle; and

operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber;

said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through said conduit means; and

control means responsive to an incipient skidding condition of a vehicle wheel for operating said adaptive braking valve means;

said operator-operated valve means being shiftable from a first position in which said pressure chamber is vented to said reservoir to a second position in which fluid communication between said pressure chamber and said reservoir means is prevented and fluid communication between said pressure source and said pressure chamber and between said adaptive braking control valve and said pressure source is permitted.

7. In a vehicle hydraulic braking system:

a pressure source and reservoir means;

hydraulic boost means in fluid communication with said pressure source and with said reservoir means;

said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means;

means communicating said another chamber to a corresponding brake of the vehicle; and

operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber;

said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through said conduit means;

said adaptive braking valve means including a housing havinga first port communicated to said another chamber, a second port communicated to said first port and to said corresponding brake of the vehicle, a third port communicated to said second port and to said reservoir means, and electrically operated valve means normally permitting communication between said first and second ports and preventing fluid communication between said second and third ports; and

control means responsive to an incipient skidding condition ofa vehicle wheel for actuating said elec trically operated valve means, whereupon fluid communication between said first and second ports is terminated and fluid communication between said second and third ports is initiated.

8. In a vehicle hydraulic braking system;

a pressure source and reservoir means;

hydraulic boost means in fluid communication with said pressure source and with said reservoir means;

said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means;

means communicating said another chamber to a corresponding brake of the vehicle; and

operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber;

said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve' means for controlling fluid communication through the conduit means; and

control means responsive to an incipient skidding condition of a corresponding vehicle wheel to actuate said adaptive braking control valve to relieve the pressure level communicated to said corresponding brake and to termination of the incipient skidding condition of the corresponding vehicle wheel to again increase the pressure level communicated to said corresponding vehicle wheel.

9. The invention of claim 7:

said adaptive braking valve means having a fourth port communicating said first port to said pressure source when said operator-actuated valve means is actuated.

10. The invention of claim 9; and

valve means within said adaptive braking control valve for normally preventing flow of fluid from said first port to said fourth port.

11. The invention of claim 8; and

means communicating pressurized fluid from said pressure source to the adaptive braking valve means when a brake application is effected to permit the pressure level at the corresponding brake to be increased upon termination of the incipient skiding condition of said corresponding wheel even though the pressure level in said another chamber is reduced. I

12. In an adaptive braking control valve for a vehicle;

a housing having first port communicated to an operator-operated fluid motor, a second port communicated to a corresponding brake of the vehicle, a third port communicated to a fluid reservoir, and electrically operated valve means normally permitting fluid communication between said first and second ports and preventing fluid communication between said first and thrid ports;

said valve means being responsive to control means responsive to acceleration of a corresponding vehicle wheel for actuating said electrically operated valve means whereupon communication between said first and second ports is terminated and communication between said first and third ports is inititated when the corresponding vehicle wheel decelerates below a predetermined rate;

said housing having a fourth port communicating said first port with a pressure source.

13. The invention of claim 12; and

valve means within said housing normally preventing flow of fluid from said housing through said fourth port.

14. In an adaptive braking control valve for a vehicle:

a housing having a first port communicated to an operator-operated fluid motor, a second port communicated to a corresponding brake of the vehicle, a third port communicated to a fluid reservoir, and electrically operated valve means normally permitting fluid communication between said first and second ports and preventing fluid communication between said first and third ports;

said valve means being responsive to control means responsive to accleration of a corresponding vehicle wheel for actuating said electrically operated valve means whereupon communication between said first and second ports is terminated and communication between said first and third ports is initiated when the corresponding vehicle wheel decelerates below a predetermined rate;

said electrically operated valve means including a normally open solenoid valve controlling communication between said first and second ports and a normally closed solenoid valve controlling comm unication between said second and third ports. 

1. In a vehicle hydraulic braking system: a pressure source and reservoir means; hydraulic boost means in fluid communication with said pressure source and with said reservoir means; said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means; means communicating said another chamber to a corresponding brake of the vehicle; and operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber; said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through said conduit means; and control means responsive to an incipient skidding condition of a vehicle wheel for operating said adaptive braking valve means.
 2. The invention of claim 1: said adaptive braking valve means having a first port communicated to said another chamber, a second port communicated to the brakes of the vehicle, and a third port communicating said electrically operated valve means to said pressure source upon actuation of said valve means.
 3. The invention of claim 2: said adaptive braking valve means having a fourth port communicating said adaptive braking valve means with said reservoir means.
 4. The invention of claim 1: said adaptive braking valve means having a first port communicated to said another chamber, a second port communicated to the vehicle brakes, and another port communicated to said reservoir means.
 5. In a vehicle hydraulic braking system: a pressure source and reservoir means; hydraulic boost means in fluid communication with said pressure source and with said reservoir means; said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means; means communicating said another chamber to a corresponding brake of the vehicle; and operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber; said pressure responsive means including means dividing said another chamber into first and second sections, each of said sections being communicated to said reservoir means; said communicating means including first conduit means communicating one of said sections to at least one of the brakes of the vehicle and seCond conduit means communicating the other section to the remaining brakes of the vehicle; first and second adaptive braking valve means, each of said adaptive braking valve means being communicated to a corresponding one of said conduit means for controlling fluid communication therethrough; and control means responsive to an incipient skidding condition of a corresponding vehicle wheel for operating said adaptive braking valve means.
 6. In a vehicle hydraulic braking system: a pressure source and reservoir means; hydraulic boost means in fluid communication with said pressure source and with said reservoir means; said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means; means communicating said other chamber to a corresponding brake of the vehicle; and operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber; said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through said conduit means; and control means responsive to an incipient skidding condition of a vehicle wheel for operating said adaptive braking valve means; said operator-operated valve means being shiftable from a first position in which said pressure chamber is vented to said reservoir to a second position in which fluid communication between said pressure chamber and said reservoir means is prevented and fluid communication between said pressure source and said pressure chamber and between said adaptive braking control valve and said pressure source is permitted.
 7. In a vehicle hydraulic braking system: a pressure source and reservoir means; hydraulic boost means in fluid communication with said pressure source and with said reservoir means; said boost means including fluid pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means; means communicating said another chamber to a corresponding brake of the vehicle; and operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber; said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through said conduit means; said adaptive braking valve means including a housing having a first port communicated to said another chamber, a second port communicated to said first port and to said corresponding brake of the vehicle, a third port communicated to said second port and to said reservoir means, and electrically operated valve means normally permitting communication between said first and second ports and preventing fluid communication between said second and third ports; and control means responsive to an incipient skidding condition of a vehicle wheel for actuating said electrically operated valve means, whereupon fluid communication between said first and second ports is terminated and fluid communication between said second and third ports is initiated.
 8. In a vehicle hydraulic braking system; a pressure source and reservoir means; hydraulic boost means in fluid communication with said pressure source and with said reservoir means; said boost means including fluId pressure responsive means defining a pressure chamber and another chamber, said another chamber being communicated to said reservoir means; means communicating said another chamber to a corresponding brake of the vehicle; and operator-actuated valve means normally venting said pressure chamber to the reservoir means, said valve means communicating said pressure source to the pressure chamber upon actuation of the valve means, whereby fluid pressure delivered to said pressure chamber operates said pressure responsive means to develop braking pressure in said another chamber; said means communicating the another chamber to the brakes of the vehicle including conduit means and adaptive braking valve means for controlling fluid communication through the conduit means; and control means responsive to an incipient skidding condition of a corresponding vehicle wheel to actuate said adaptive braking control valve to relieve the pressure level communicated to said corresponding brake and to termination of the incipient skidding condition of the corresponding vehicle wheel to again increase the pressure level communicated to said corresponding vehicle wheel.
 9. The invention of claim 7: said adaptive braking valve means having a fourth port communicating said first port to said pressure source when said operator-actuated valve means is actuated.
 10. The invention of claim 9; and valve means within said adaptive braking control valve for normally preventing flow of fluid from said first port to said fourth port.
 11. The invention of claim 8; and means communicating pressurized fluid from said pressure source to the adaptive braking valve means when a brake application is effected to permit the pressure level at the corresponding brake to be increased upon termination of the incipient skiding condition of said corresponding wheel even though the pressure level in said another chamber is reduced.
 12. In an adaptive braking control valve for a vehicle; a housing having first port communicated to an operator-operated fluid motor, a second port communicated to a corresponding brake of the vehicle, a third port communicated to a fluid reservoir, and electrically operated valve means normally permitting fluid communication between said first and second ports and preventing fluid communication between said first and thrid ports; said valve means being responsive to control means responsive to acceleration of a corresponding vehicle wheel for actuating said electrically operated valve means whereupon communication between said first and second ports is terminated and communication between said first and third ports is inititated when the corresponding vehicle wheel decelerates below a predetermined rate; said housing having a fourth port communicating said first port with a pressure source.
 13. The invention of claim 12; and valve means within said housing normally preventing flow of fluid from said housing through said fourth port.
 14. In an adaptive braking control valve for a vehicle: a housing having a first port communicated to an operator-operated fluid motor, a second port communicated to a corresponding brake of the vehicle, a third port communicated to a fluid reservoir, and electrically operated valve means normally permitting fluid communication between said first and second ports and preventing fluid communication between said first and third ports; said valve means being responsive to control means responsive to accleration of a corresponding vehicle wheel for actuating said electrically operated valve means whereupon communication between said first and second ports is terminated and communication between said first and third ports is initiated when the corresponding vehicle wheel decelerates below a predetermined rate; said electrically operated valve means including a normally open solenoid valve controlling communication between said first and second ports and a normally closed solEnoid valve controlling communication between said second and third ports. 